1. Field of the Invention
This invention relates to an electrophotographic photoconductor using a specific phthalocyanine as a charge generating agent.
This invention aims to provide an electrophotographic material of excellent performance by using, as a charge generating agent, modified chlorinated aluminum phthalocyanine crystals excellent in charge generating property and by combining this charge generating agent with a charge transfer agent.
2. Description of the Prior Art
Since Carlson invented an electrophotographic photoconductor, numerous photoconductors have been developed and have been used in many fields such as copying machines, photograving machines, and printers. Particularly in recent years, these electrophotographic photoconductors are making remarkable developments in the field of printers. A multi-purpose electrophotographic photoconductor which conforms not only to the light source of a semiconductor laser but also to light sources such as, for example, a light-emitting diode and an He/Ne gas laser has been demanded.
As means of meeting this requirement, various inorganic and organic photoconductors have been proposed. As inorganic type photoconductors, amorphous silicon, selenium-tellurium compound, and selenium-arsenic compound have been known to the art. As organic type photoconductors, various materials using phthalocyanines, condensed polycyclic compounds, azo type pigments, and other coloring matters as charge generating agents and combining these charge generating agents with various charge transfer agents have been known to the art.
These photoconductors, to be suitable for light sources of semiconductor lasers or light-emitting diodes, require a charge generating agent capable of efficiently absorbing the semiconductor laser beam or the light-emitting diode beam and excellent in charge generating property.
Phthalocyanines which are one species of organic photoconductors find utility in many applications because they have an absorption wavelength range extended to a long wavelength and possess a highly satisfactory charge generating ability as compared with other photoconductors.
What is particularly noted about photoconductors using phthalocyanines is the fact that these phthalocyanines are used in the form of specific crystals as a charge generating agent.
For example, the same metal-free phthalocyanines are known to be useful in varying crystal forms such as the X form which is described in British Patent No. 1,116,553, the .tau. and .eta. forms which are shown in U.S. Pat. No. 4,507,374, and the .alpha. and .beta. forms which are described in J. Phys. Chem., 27, 3230 (1968). Also, copper phthalocyanine is known to be used in various crystal forms such as, for example, the .epsilon. form which is described in Japanese Patent Publication No. 1667/1977, and the .alpha., .beta., .gamma., .pi., .chi., and .rho. forms. It has been known that this difference in crystal form brings about variations of photoconductivity. In selecting from among various phthalocyanines a specific phthalocyanine for use as a charge generating agent in a photoconductor, the specific phthalocyanine must contain a crystal structure which is exactly defined and established to be effective in generating a charge in the photoconductor.
It has been known that photoconductors using, as charge generating agents, the crystals of chlorinated aluminum phthalocyanines represented by chloroaluminum phthalocyanine and chloroaluminum phthalocyanine chloride among other phthalocyanines described above are particularly useful as electrophotographic photoconductors operating with various light sources because they exhibit high spectral sensitivity to long wavelengths in the visible range in the neighborhood of 500 nm through the near-infrared range of 900 nm. For example, Ivanof Chemical Engineering Research Report (dated Feb. 2, 1972) contains in pp. 1905 to 1908 a statement which purports that chloroaluminum phthalocyanine shows photoconductivity. British Patent No. 1,268,574 discloses that polychloroaluminum phthalocyanine can be used as an electrophotographic photoconductor. It is stated in Japanese Patent Application Laid-open No. 211149/1982 and U.S. Pat. No. 4,426,434 that the aluminum phthalocyanine which is obtained by treating with a vacuum deposited solvent a film containing chloroaluminum phthalocyanine or chloroaluminum phthalocyanine chloride and which possesses a specific X-ray diffraction spectrum and infrared absorption spectrum is useful as a charge generating layer in a layered photoconductor possessing high sensitivity in the near-infrared range.
The present inventors made a study on an electrophotographic photoconductor using chloroaluminum phthalocyanine chloride represented by the formula, AlClC.sub.32 N.sub.8 H.sub.( 15.6-14.4)Cl.sub.( 0.4-1.6), as a charge generating agent. They have consequently found that the phthalocyanine in a form merely vacuum deposited on a film or applied by dispersion of fine particles on a film possesses an insufficient charge generating ability and that this phthalocyanine, when treated with a solvent such as toluene, xylene, or chloroform which possesses affinity for phthalocyanines, gives rise to a chloroaluminum phthalocyanine chloride possessing a specific X-ray diffraction and exhibiting an excellent charge generating ability in the visible range through the near-infrared range (U.S. Pat. No. 4,444,861).
However, the performance of the photoconductor actually obtained by the procedure just described varies and constant characteristics are obtained only with difficulty. While it enjoys high sensitivity, it entails the disadvantage that it has high residual potential and induces an unwanted phenomenon of fogging in actual printing.